1. Technical Field
The present invention relates to power control. More particularly, the present invention relates to a method, a program and an apparatus for power control of a magnetic disk unit through an electronic information device provided with the power control apparatus.
2. Description of the Related Art
Conventionally, a magnetic disk unit such as a hard disk drive has been used as auxiliary equipment of an electronic information device, such as a computer. Such a disk device has multiple power consumption configurations and lowers its power consumption by appropriately switching configurations. The multiple power consumption configurations are different in terms of processing time between receipt and completion of a write instruction or a read instruction. The processing times include a time necessary to perform an instruction to shift into a particular configuration for low power consumption, a time necessary to perform a configuration shift in response to a write instruction or a read instruction (to allow performance of the instruction), and a time necessary to perform an instruction after shifting configurations. Therefore, it is necessary to appropriately switch configurations so as not to increase the processing time.
One prior-art power consumption control technique involves a power consumption timer that is provided in an information processing apparatus. In that technique, a set value of the power consumption timer is adaptively changed such that power consumption is reduced without compromising the throughput of the information processing apparatus. The information processing apparatus can be placed in power saving mode after a set time in the power consumption timer has elapsed. If a task resume request is issued within a configurable time after the information processing apparatus enters power saving mode, the set time in the power consumption timer is increased to prevent subsequent unnecessary entry into power saving mode.
The technology described above changes the power consumption timer according to the transition time between (low-power consumption) power saving mode and operational mode and according to the elapsed time required for completion of processing. However, in the prior art, the elapsed time before a transition to low-power consumption mode is determined is not taken into consideration. In particular, if the time required for the apparatus transitions to low-power consumption mode varies depending on situations at the time of transition, the value of the timer can be improperly set in some situations, and thus can reduce the throughput of the apparatus.
What is needed is a method to provide a power control for a magnetic disk unit that performs mode switching in a manner proper to the situation at transition to low-power consumption mode so that power consumption is efficiently reduced without decreasing the throughput of the magnetic disk unit.